Circles Shape and Space

Formula for the area of a circle We can find the area of a circle using the formula radius Area of a circle = πr 2 Area of a circle = π × r × r or

The circumference of a circle Use π = 3.14 to find the area of this circle. A = πr 2 4 cm = 3.14 × 4 × 4 = cm 2

Finding the area given the diameter The radius of a circle is half of its radius, or We can substitute this into the formula A = πr 2 to give us a formula to find the area of a circle given its diameter. r = d 2 A = πd2πd2 4

The area of a circle Use π = 3.14 to find the area of the following circles: A = πr 2 2 cm = 3.14 × 2 2 = cm 2 A = πr 2 10 m = 3.14 × 5 2 = 78.5 m 2 A = πr 2 23 mm = 3.14 × 23 2 = mm 2 A = πr 2 78 cm = 3.14 × 39 2 = cm 2

Find the area of this shape Use π = 3.14 to find area of this shape. The area of this shape is made up of the area of a circle of diameter 13 cm and the area of a rectangle of width 6 cm and length 13 cm. 6 cm 13 cm Area of circle = 3.14 × = cm 2 Area of rectangle = 6 × 13 = 78 cm 2 Total area = = cm 2